The present invention relates to a color filter for reflection-type liquid crystal display devices, which is used in color liquid crystal display devices, color input devices, etc., and to a reflection-type liquid crystal display device comprising the color filter.
Color liquid crystal display devices include transmission-type color liquid crystal display devices and reflection-type color liquid crystal display devices, all of which are driven in an electric field, with saving power, and give high-quality images such as those typically in TFT liquid crystal display devices. Therefore, they are being much highlighted as display devices favorable to the recent multimedia technology.
For obtaining satisfactory light images, in general, much used are light-incorporating, transmission-type liquid crystal display devices of a backlight or sidelight type in which is disposed a light source (of a lamp such as a fluorescent micro-lamp or the like), for example, on the back or side of the liquid crystal panel. However, the transmission-type liquid crystal display devices of that kind require much power for the lamp therein, and lose the advantages of power-saving, lightweight and portable characteristics intrinsic to liquid crystal display devices.
On the other hand, for lighting the liquid crystal display panel in reflection-type liquid crystal display devices, used is reflecting room light or external light as the light source. Therefore, the devices do not require a lamp to be built therein, and their display panel could be thinned. In addition, the battery life for them could be prolonged. For these reasons, they are ideal power-saving display devices. Further, as being lightweight, they are handy for mobile display devices.
FIG. 4 shows a cross section of a conventional, reflection-type liquid crystal display device. As illustrated, the device comprises a (first) substrate 41 on the light reflection side and a (second) substrate 42 on the light input side, which are so disposed as to face each other via a liquid crystal layer 48 being sandwiched therebetween; a reflection electrode 43 formed on the first substrate 41 to face the liquid crystal layer; a color filter which is composed of a colorant layer 44 of red (R), green (G) and blue (B) formed on the second substrate 42 to face the liquid crystal layer, a light-shielding layer 45 formed between the adjacent colorants, a planar layer 46 formed on the colorant layer 44 and the light-shielding layer 45, and a transparent electrode 47 formed on the planar layer 46; and a polarizing plate 49 disposed on the outer surface of the second substrate 42.
In the liquid crystal display device illustrated, however, the color filter is disposed on the light input side, and the colorant layer of the color filter is spaced from the reflection electrode via a gap therebetween. Therefore, in the device, the light having reflected on the reflection electrode shall pass through a site of the colorant layer which differs from that through which the incident light has passed, owing to the gap between the colorant layer and the reflection electrode, there by causing color drift (colormixing) in the images formed. In addition, in the device, the width of the light-shielding layer to be between the adjacent colorants must be large in order to evade light leakage, with the result that the aperture is reduced and images with satisfactory brightness could not be obtained. Moreover, in fabricating the device, it is necessary to align the position of the color layer on the light input side with that of the reflection electrode on the light reflection side, and the yield in the device fabrication is poor.
Another reflection-type liquid crystal display device (FIG. 5) has been proposed. The device comprises a first substrate 51 on the light reflection side; a reflection electrode 53 formed on the first substrate 51 to face a liquid crystal layer; a color filter composed of a colorant layer 54 and a transparent electrode 56 and formed on the reflection electrode in that order; a second substrate 52 on the light input side; another transparent electrode 56 formed on the second substrate 52 to face the liquid crystal layer; and a polarizing plate formed on the outer surface of the second substrate 52. In the device, however, contact through-holes 59 must be formed through the colorant layer, via which the reflection electrode of being a pixel electrode is electrically connected with the transparent electrode (liquid crystal driving electrode) 56 formed on the surface of the colorant layer. Forming the contact through-holes requires a complicated process, with the result that the yield in the device fabrication is poor. In addition, in the device, ITO (indium oxide doped with tin oxide; indium tin oxide) is generally used for forming the transparent electrode to be on the surface of the colorant layer. Therefore, where the reflection electrode is of an aluminium-based metallic substance, impurities, if any, around the electrodes will induce local cell reaction between aluminium and ITO through the contact through-holes, thereby causing interconnection breakdown. As the case may be, aluminium constituting the reflection electrode will then be blackened. In that condition, the device could not enjoy satisfactory light reflection. For these reasons, the device is still defective.
The present invention has been made in consideration of the problems noted above, and its object is to provide an improved color filter for reflection-type liquid crystal display devices, and to provide a reflection-type liquid crystal display device comprising it. With the color filter, the reflection-type liquid crystal display device of the invention is not troubled by color drift (color mixing), and enjoys a broad angle of visibility. In addition, even when driven for a long period of time, the device is not troubled by interconnection breakdown and reflectance depression, and all the time can produce light images.
In order to attain the object as above, the invention provides a color filter for reflection-type liquid crystal display devices, which comprises a light-reflecting layer, a transparent electrode, and a colorant layer containing fine electroconductive grains therein, as laminated in that order on a transparent or opaque substrate.
In one preferred embodiment of the color filter, the light-reflecting layer is of a metallic substance comprising aluminium as the essential component.
In another preferred embodiment of the color filter, the transparent electrode is of an amorphous electroconductive metal oxide compound comprising indium oxide and zinc oxide as the essential components.
The invention further provides a reflection-type liquid crystal display device, which comprises a first substrate and a second substrate as so disposed that they face each other via a liquid crystal layer existing therebetween, a color filter comprising a light-reflecting layer, a transparent electrode and a colorant layer with fine electroconductive grains therein as laminated in that order on the first substrate to face the liquid crystal layer, a transparent electrode formed on the second substrate to face the liquid crystal layer, and a polarizing plate formed on the outer surface of the second substrate.